1. Technical Field of the Invention
The present invention relates to a transflective liquid crystal device. More particularly, the present invention relates to a multi-gap type liquid crystal device in which the layer thickness of a liquid crystal layer between a transmissive display region and a reflective display region within a single pixel, has been changed into an appropriate value.
2. Description of the Related Art
Among a variety of liquid crystal devices, ones that are capable of displaying images both in a transmissive mode and in a reflective mode are referred to as “transflective liquid crystal devices”, and are used in all scenes.
As shown in FIGS. 21A to 21C, the transflective liquid crystal device comprises a transparent first substrate 10 with first transparent electrodes 11 formed on the surface thereof, a transparent second substrate 20 with second transparent electrodes 21 formed on its surface side opposed to the first electrodes 11, and a TN (Twisted Nematic) mode liquid crystal layer 5 held between the first substrate 10 and the second substrate 20. On the first substrate 10, light reflecting layers 4 each constituting a reflective display region 31 is formed in one of pixel regions 3 where the first transparent electrodes 11 and the second transparent electrodes 21 are opposed. The remaining regions where the light reflecting layers 4 are not formed, each constitutes a transmissive display region 32. Polarizers 41 and 42 are disposed on the outer surfaces of the first and second substrates 10 and 20, respectively. A backlight device 7 is opposed to the polarizer 41 side.
In the liquid crystal device 1 with this arrangement, out of light emitted from the backlight device 7, the light made incident on the transmissive display region 32 enters the liquid crystal layer 5 from the first substrate 10 side, as indicated by the arrow L1. After having been subjected to an optical modulation at the liquid crystal layer 5, the light is emitted from the second substrate 20 side as transparent display light, thereby displaying an image (transmissive mode).
Also, out of external light made incident from the second substrate 20 side, the light entering the reflective display region 31 reaches the reflective layer 4 through the liquid crystal layer 5, as indicated by the arrow 2. After having been reflected from the reflective layer 4, the light again passes through the liquid crystal layer 5, and is emitted from the second substrate 20 side as a reflective display light, thereby displaying an image (reflective mode).
On the first substrate 10, a reflective display color filter 81 and a transmissive display color filter 82 are formed in each of the reflective display regions 31 and each of the transmissive regions 32, respectively, thereby allowing color display.
When performing such an optical modulation, if the twisted angle of a liquid crystal is set to be small, the change in a polarization condition becomes a function of the product of a difference in the refractive index Δn and a layer thickness d of the liquid crystal layer 5, i.e., the retardation Δn·d. Therefore, making this value an appropriate one allows the achievement of the display giving high visibility. However, in the transflective liquid crystal device 1, the transmissive display light only once passes through the liquid crystal layer 5 and is emitted, whereas the reflective display light twice passes through the liquid crystal layer 5, and therefore, it is difficult to optimize the retardation Δn·d for both the transmissive display light and the reflective display light. Hence, if the layer thickness d of the liquid crystal layer 5 is set so that the display in a reflective mode has high visibility, the display in a transmissive mode will be sacrificed. Conversely, if the layer thickness d of the liquid crystal layer 5 is set so that the display in a transmissive mode has high visibility, the display in a reflective mode will be sacrificed.
Accordingly, Japanese Unexamined Patent Application Publication No. 11-242226 discloses a configuration in which the layer thickness d of the liquid crystal layer 5 in the reflective display region 31 is less than that of the liquid crystal layer 5 in the transmissive display region 32. Such a configuration is referred to as a “multi-gap type”. For example, as shown in FIGS. 21A to 21C, this type of configuration can be implemented by a layer-thickness adjusting layer 6 in which a region corresponding to the transmissive display region 32 constitutes an opening, on the lower layer side of the first transparent electrode 11, and on the upper layer side of the light reflecting layer 4. More specifically, in the transmissive display region 32, the layer thickness d of the liquid crystal layer 5 is larger than in the reflective display region 31 by the layer thickness of the layer-thickness adjusting layer 6, and hence, it is possible to optimize the retardation Δn·d for both the transmissive display light and the reflective display light. Herein, in order to adjust the layer thickness d of the liquid crystal layer 5 by the layer-thickness adjusting layer 6, it is necessary to thickly form the layer-thickness adjusting layer 6. A photoresist or the like is used to form such a thick layer.
While a photolithography technique is used when the layer-thickness adjusting layer 6 is formed with a photoresist, the layer-thickness adjusting layer 6 becomes an upwardly inclined surface 60 in the boundary region of the reflective display region 31 and the transmissive display region 32, due to problems such as the exposure accuracy when performing the photolithography, the side etching during development. As a result, in the boundary portion of the reflective display region 31 and the transmissive display region 32, the layer thickness d of the liquid crystal layer 5 continuously varies, so that the retardation Δn·d continuously varies, as well. As for the liquid crystal molecules contained in the liquid crystal layer 5, the initial alignment condition is defined by alignment films 12 and 22 formed on the outermost layers of the first and second substrates 10 and 20, respectively. However, on the inclined surface 60, since the alignment regulating force on the alignment film 12 acts in an oblique direction, the alignment of the liquid crystal molecules in this portion is disturbed.
Even if the above-described boundary portion does not constitute an inclined surface, there is the possibility that the substrate and a stepped portion orthogonally intersect each other, thereby disturbing the alignment of the liquid crystal molecules.
As a consequence, in the conventional liquid crystal device 1, when it is designed, for example, as a normally white type, although the full screen must become black display with an electric field applied, light leaks from the portion corresponding to the inclined surface 60, thereby causing a display failure such as a reduction in the contrast.
To solve the above-described problems, the object of the present invention is to provide an arrangement capable of performing high-quality display even if the retardation is in an inappropriate condition, or the alignment of liquid crystal molecules is in a disturbed condition in the boundary portion of the transmissive display region and the reflective display region, in a multi-gap type liquid crystal device in which the layer thickness of the liquid crystal layer between the transmissive display region and the reflective display region within a single pixel has been changed into an appropriate value, and in an electronic device using the same.